Technical Field
The present invention relates to a pigment dispersion and a method of producing the pigment dispersion.
Background Art
In recent years, with the progress in inkjet recording technology, an inkjet recording method has become to be used for highly precise images such as photographs or off-set printings. Therefore, high-quality recording in accordance with an inkjet recording method is demanded.
With regard to such demands, as a method of producing an ink which exhibits excellent dispersion stability and provides printed matter having excellent color forming property and also excellent transparency, a method has been proposed, which includes a process of obtaining a solution containing a dispersing agent and a water insoluble coloring material dissolved in an aprotic organic solvent in the presence of alkali, a process of mixing this solution with water, to obtain a dispersion in which particles containing the water insoluble coloring material and the dispersing agent are dispersed, a process of adding an acid to the dispersion to form an aggregate, and separating the aggregate, and a process of performing alkali treatment to re-disperse the particles of the aggregate (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2004-43776).
Further, in ink compositions formed by using a polymerizable compound and a pigment dispersion, as an ink composition which has excellent discharge reliability over a long period of time and can form an image without defects such as image voids, an ink composition including a pigment covered with a dispersion polymer that is obtained by crosslinking a water soluble dispersing agent using a crosslinking agent, a water soluble polymerizable compound, a polymerization initiator, and water has been proposed (see, for example, JP-A No. 2011-231315).
As a pigment dispersion in which a pigment is finely dispersed and in which the dispersion stability of the pigment is excellent even in a case in which the pigment dispersion is stored for a long time, a pigment dispersion including a pigment, a polymer which contains a repeating unit with a specific structure having a resin acid derivative and has a weight average molecular weight within a range of from 10,000 to 1,000,000, and a polymerizable compound has been proposed (see, for example, JP-A No. 2010-7020).
As a finer and more stable pigment dispersion, a pigment dispersion which is formed by dispersing a pigment in water, the pigment surface being in an acidic state, using an anionic surface active agent as a dispersing agent and which can also be used for inkjet recording has been proposed (see, for example, JP-A No. 2010-96876).